1. Field of the Invention
The present invention relates to a beam scanning apparatus of an electrophotographic color printer.
2. Description of the Related Art
FIG. 1 shows a general electrophotographic color printer. Referring to the drawing, an electrophotographic color printer includes a photoreceptor, such as a photoreceptor belt 1, and a beam scanning apparatus 30 for exposing the photoreceptor belt 1 to light to form an electrostatic latent image. Developing units 21, 22, 23, and 24 develop the electrostatic latent image.
During operation, the photoreceptor belt 1 circulates around guide rollers 3. An image record surface of the photoreceptor belt 1 is exposed by a beam emitted from the beam scanning apparatus 30. The beam scanning apparatus 30 is positioned at the upstream side of each of the developing units 21-24 which develop the electrostatic latent.
The respective developing units 21-24 develop images of different colors, e.g., yellow, magenta, cyan, and black. The developed image is dried by a drying unit 8 and then transferred via a transfer roller 9 to a paper 10 passing between the transfer roller 9 and a fusing roller 11. The electrostatic latent image remaining on the photoreceptor belt 1 is removed by a reset unit 2.
FIG. 2 shows a conventional beam scanning apparatus which is adopted in the above electrophotographic color printer to expose the photoreceptor to light. Referring to the drawing, the conventional beam scanning apparatus 30 includes a light source 31, a beam deflector 34 for deflecting light emitted from the light source 31, and an f-.theta. lens 37 for correcting an error of the light deflected by the beam deflector 34.
Also, a focusing lens 33 for focusing the divergent beam emitted from the light source 31 is provided between the light source 31 and the beam deflector 34. A mirror 38 for changing a path of the beam is provided between the beam deflector 34 and the photoreceptor (not shown). The focusing lens 33 determines the size of an optical spot formed on the photoreceptor.
The beam deflector 34 includes a motor 35 and a rotary polygonal mirror 36 which is rotated by the motor 35. The beam input to the beam deflector 34 is deflected according to an angle made between a reflection surface of the rotary polygonal mirror 36 and the input beam.
In the beam scanning apparatus 30 having the above structure, the photoreceptor is exposed to light by a main scanning direction by the beam deflector 34 and a sub-scanning direction by the movement of the photoreceptor 1 which is perpendicular to the main-scanning direction.
However, the above structure of the beam scanning apparatus 30 having the rotary polygonal mirror 36 and the motor 35 is complicated. Further, in a color printer, the beam scanning apparatus 30 is required for each color formed into a color image, thereby increasing the size of the apparatus.